1. Field of the Invention
This invention relates to a rear converter lens, particularly to a rear converter lens having the function of a macro-lens.
2. Description of the Prior Art
When the function of a macro-lens is given to a camera, it is known that the photographic objective is fitted with an extention tube or a special rear converter lens. Since the whole lens is made to shift without changing the interval between the rear and front mount of the converter in these kinds of known rear converter lens, the lens will approach nearer to the surface of a film as the magnification of lens is made higher. Consequently, the lens back should be made considerably long and the total length of the converter lens becomes longer, resulting in that it is unhandy to carry. To shorten the total length of the converter lens, the total length of lens formation should be made shorter, and number of lenses should be made smaller, so that good correcting aberrations will become difficult. Further, in such a known type that the whole lens is made to move, photographing with magnification from 1:.infin. to 1:1 could not be effected.
Among known cameras, there are those in which for transmitting the F number at open aperture of the photographing lens (the master lens) to the camera body, a signal pin having the height corresponding to the F number at open aperture is projectingly provided on the rear portion of the lens, and this pin is made to abut on a receiving piece on the side of camera body. Therefore, in the rear converter lens used for these kinds of cameras, an interconnecting rod communicating from the side of the master lens to the side of the camera body is provided to make the length of the interconnecting rod equal to the length of the interval between the rear and front mount. The signal pin provided on the mater lens is made to abut on one end of the interconnecting rod, the other end of which is made to project on the side of the camera body by the same amount as the height of the signal pin. Thereby the F number at open aperture of the master lens is transmitted to the side of the camera body. While, in the rear converter lens, in which the interval between the rear and front mount is varied, such an interconnecting system as mentioned above cannot be used.